1. Field of the Invention
The present invention relates to an image forming method for a copying apparatus or printer employing an electrophotographic method, and more particularly to a method for developing with a toner an electrostatic latent image formed on a photosensitive member.
2. Description of the Prior Arts
In order to perform a copying operation by using a copying apparatus or the like, firstly formed on a photosensitive member is an electrostatic latent image having a pattern corresponding to a document's image. Thereafter, the latent image is made visible to form a toner image with a developer which contains toner, and then, the toner image is transferred onto a transfer material.
Further, in an electrophotographic printer such as a laser beam printer or the like, an electrostatic latent image formed by scanning an output content onto a photosensitive member with a semiconductive laser light is made visible by the same manner as mentioned above.
Conventionally, inorganic materials such as Se, CdS, ZnO or the like are employed for a photosensitive member for use in such a copying apparatus, printer and the like. Further, the use of organic materials for a photosensitive member has been increasing recently.
Of these photosensitive members, amorphous selenium photosensitive members have some problems with respect to heat resistance, spectral sensitivity and dark decay. In order to overcome these problems, arsenic is doped into a selenium layer or a selenium-tellurium layer is laminated on the selenium layer. As a result, the amorphous selenium photosensitive members have the highest photosensitivity in spectral luminous efficiency of all the members and members comprising a selenium layer having a selenium-tellurium layer laminated thereon have the highest sensitivity in long wavelength light which is required for a printer using semiconductive laser light as a light source.
On the other hand, organic photosensitive members are excellent from the standpoints of sensitivity, chargeability and cost for manufacture.
Materials used in the construction of organic photosensitive members are, in general, photoconductive materials which produce an electric charge such as, for example, phthalocyanine series pigments, azo series pigments, perillene series pigments and the like, electrical charge transporting materials such as, for example, triphenylmethanes, triphenylamines, hydrazones, styryl compounds, pyrazolines, oxazoles, oxydiazoles, and the like, binding materials for dispersion coating such as, for example, polyester, polyvinyl butyral, polycarbonate, polyarylate, phenoxy, styrene-acryl, and other resins.
Repeated use of these types of photosensitive members, however, gives rise to problems of image defects, white streaks, and the like. These problems arise because the surface hardness of the organic photosensitive member roughly falls within the range from the 5B to B levels of the JIS standards for pencil lead hardness although the selenium-arsenic and selenium-tellurium photosensitive members have the surface hardness of about H, thus the surface of the photosensitive member is readily damaged due to the friction which is generated when the member comes into contact with the transfer paper, cleaning components, developer, and the like. Another cause of such problems is the harsh surface contact made when paper jams occur and the resultant reversion to manual operation required to remedy the malfunction. Furthermore, damage to the surface of the photosensitive member results in a marked reduction in the surface potential of the member.
Moreover, the selenium members have a disadvantage that they are harmful to the human body. Specifically, selenium and arsenic which are scraped or vaporized by a heat in the copying apparatus are very harmful to the human body, the harmfulness of said substances being a matter for concern.
The inventors of the present invention have proposed in U.S. Ser. No. 069,516 filed July 2, 1987 (Group Art Unit: 156) a photosensitive member having a hard surface protective layer formed on the surface of a photosensitive member in order to overcome these problems. More specifically, U.S. Ser. No. 069,516 discloses a photosensitive member having an overcoat layer of amorphous hydrocarbon containing halogen atoms formed on the photosensitive member, said overcoat layer being formed by using hydrocarbon gases and halogen compound gases as a starting material and by causing a glow discharge under a vacuum.
However, the photosensitive member having the surface protective layer is low in moisture resistance when repeatedly used, causing a problem of producing an image drift during the development.